The increasing utilization of microwave communication systems for the transmission of data has created a substantial need for a bendable wave guide exhibiting both low losses and uniform electrical characteristics in the millimeter microwave region. This need is especially acute in systems operating in the 20-150 GHz. range where space considerations or mechanical limitations do not always permit the transmission of microwave energy from one item of equipment to another along a straight line path.
A number of flexible wave guides are currently being used in the microwave industry. One of the commonly used prior art flexible wave guides is the interlocking type which is made by spirally winding a strip of metal whose edge portions are folded and compressed during winding to form a continuous interlocking structure. During flexure, the interlocking edges slide over each other, allowing the wave guide to assume the desired shape.
This particular type of wave guide can be made with any desired cross-sectional shape, but is usually formed with a rectangular cross section insofar as the polarization characteristics of this cross-sectional shape are the easiest with which to design. Although an interlocking wave guide fabricated in this manner works well at lower frequencies, the irregularities of its inner surface cause its performance to precipitously decline at higher frequencies.
In an attempt to improve upon this type of flexible wave guide, some wave guides have been designed which include an interlock configuration which does not permit sliding. At the same time, U-shaped convolutions or corrugations between the interlocks are provided. The corrugations expand open, compensating for the loss of flexibility caused by the inability of the interlock structure to slide. See, for example, U.S. Pat. No. 3,331,400. However, even this wave guide structure is unsuitable for use in the 20-150 GHz. range. The fabrication of the convoluted wave guide invariably results in a wave guide which includes large irregularities which cause unacceptable attenuation in the millimeter microwave region due to the impossibility of manufacturing a wave guide having small enough convolutions to operate efficiently in the higher frequency microwave regions.